Systems and methods for low latency 3-axis accelerometer calibration

ABSTRACT

Systems and methods for low-latency calibration of the alignment of 3-axis accelerometers in accordance embodiments of the invention are disclosed. In one embodiment of the invention, a telematics system includes a processor, an acceleration sensor, a velocity sensor, and a memory configured to store an acceleration alignment application, wherein the acceleration alignment application configures the processor to determine vehicular forward acceleration information and vehicular lateral acceleration information, calculate a lateral acceleration vector, a forward acceleration vector, and a vertical acceleration vector using a forward incline vector and a lateral incline vector determined using the vehicular forward acceleration information and vehicular lateral acceleration information.

CROSS REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. patent applicationSer. No. 13/770,917 entitled “Systems and Methods for Low Latency 3-AxisAccelerometer Calibration” to Hergesheimer et al., filed Feb. 19, 2013,the disclosure of which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is generally related to calibrating the alignmentof a 3-axis accelerometer and more specifically to the low latencycalibration of 3-axis accelerometers to align with a vehicle's axis.

BACKGROUND OF THE INVENTION

A Global Positioning System (GPS) is a space based global navigationsatellite system that utilizes a network of geo-synchronous satellitesthat can be utilized by a GPS receiver to determine its location. Manytelematics systems incorporate a Global Positioning System (GPS)receiver, which can be used to obtain the location of a vehicle at acertain measured time. Using the signals received by the GPS receiver,the heading information of the vehicle can be determined. A GPS receivercan determine velocity information in a variety of ways including, butnot limited to, measuring the Doppler shift of the received signals andby comparing the location of a vehicle at a plurality of measured times.The acceleration of the vehicle can be determined as the change in speeddivided by the time between the measurements. A GPS receiver's abilityto determine acceleration can be limited due to the dependence of themeasurement upon factors such as, but not limited to, reception andsatellite availability. In addition to location information, a GPSreceiver can also be configured to provide time data. However,measurements determined via a GPS receiver can contain errors thataffect the accuracy of the measured information. In particular, GPSsignals are vulnerable to signal delays, inconsistencies of atmosphericconditions that affect the speed of the GPS signals as they pass throughthe Earth's atmosphere, and multipath distortions. Additionally, otherfactors not listed above can influence GPS signals and result inmeasurement errors.

An accelerometer is a device that measures acceleration associated withthe weight experienced by a test mass in the frame of reference of theaccelerometer device. The acceleration measured by an accelerometer istherefore a weight per unit of test mass, or g-force. Thereby, astationary accelerometer in a vehicle would experience the earth'sgravity while a free falling one would not.

SUMMARY OF THE INVENTION

Systems and methods for low latency calibration of the alignment of3-axis accelerometers in accordance embodiments of the invention aredisclosed. In one embodiment of the invention, a telematics systemincludes a processor, an acceleration sensor connected to the processorand configured to determine forward acceleration information along aforward axis, lateral acceleration information along a lateral axis, andvertical acceleration information along a vertical axis, a velocitysensor connected to the processor and configured to determine velocityinformation along a vehicular forward axis and heading information, anda memory connected to the processor and configured to store anacceleration alignment application, wherein the acceleration alignmentapplication configures the processor to determine vehicular forwardacceleration information along the vehicular forward axis using thevelocity information, determine vehicular lateral accelerationinformation using the velocity information and the heading information,calculate a lateral acceleration vector using the forward accelerationinformation, the lateral acceleration information, the verticalacceleration information, and the vehicular lateral accelerationinformation, calculate a forward acceleration vector using the lateralacceleration vector and the vehicular forward acceleration information,calculate a vertical acceleration vector using the lateral accelerationvector and the forward acceleration vector, compute lateral alignmentinformation using the lateral acceleration vector, the forwardacceleration information, the lateral acceleration information, and thevertical acceleration information, compute forward alignment informationusing the forward acceleration vector, the forward accelerationinformation, the lateral acceleration information, and the verticalacceleration information, an compute vertical alignment informationusing the vertical acceleration vector, the forward accelerationinformation, the lateral acceleration information, and the verticalacceleration information.

In an another embodiment of the invention, the acceleration alignmentapplication further configures the processor to calculate the lateralacceleration vector by determining a lateral incline vector using acalibrated forward vector, the forward acceleration information, thelateral acceleration information, the vertical acceleration information,and the vehicular lateral acceleration information and calculating thelateral acceleration vector using the calibrated forward vector and thelateral incline vector.

In an additional embodiment of the invention, the calibrated forwardvector aligns the vehicular forward axis with the forward axis.

In yet another additional embodiment of the invention, the accelerationalignment application further configures the processor to determine avehicular lateral axis using the heading information and the vehicularforward acceleration information and the calibrated forward vectorfurther aligns the vehicular lateral axis with the lateral axis.

In still another additional embodiment of the invention, the lateralacceleration vector is the normalized cross product of the calibratedforward vector and the lateral incline vector.

In yet still another additional embodiment of the invention, theacceleration alignment application further configures the processor tocalculate the forward acceleration vector by determining a forwardincline vector using the lateral acceleration vector, the lateralincline vector, the vehicular forward acceleration information, theforward acceleration information, the lateral acceleration information,and the vertical acceleration information and calculating the forwardacceleration vector using the forward incline vector and the lateralacceleration vector.

In yet another embodiment of the invention, the forward accelerationvector is the normalized cross product of the forward incline vector andthe lateral acceleration vector.

In still another embodiment of the invention, the acceleration alignmentapplication further configures the processor to calculate the verticalacceleration vector using the lateral acceleration vector and theforward acceleration vector.

In yet still another embodiment of the invention, the verticalacceleration vector is the normalized cross product of the lateralacceleration vector and the forward acceleration vector.

In yet another additional embodiment of the invention, the accelerationsensor is a 3-axis accelerometer and the acceleration sensor isconfigured to determine an acceleration sensor vector including theforward acceleration information, the lateral acceleration information,and the vertical acceleration information.

Still another embodiment of the invention includes a method forcalibrating acceleration information using a telematics system, wherethe telematics system is mounted in the vehicle having a vehicularforward axis, a vehicular lateral axis, and a vehicular vertical axis,including determining vehicular forward acceleration information along avehicular forward axis using the telematics system, determiningvehicular lateral acceleration information along a vehicular lateralaxis using the telematics system, calculating a lateral accelerationvector using the vehicular lateral acceleration information using thetelematics system, calculating a forward acceleration vector using thelateral acceleration vector and the vehicular forward accelerationinformation using the telematics system, calculating a verticalacceleration vector using the lateral acceleration vector and theforward acceleration vector using the telematics system, computinglateral alignment information using the lateral acceleration vectorusing the telematics system, computing forward alignment informationbased on the forward acceleration vector using the telematics system,and computing vertical alignment information based on the verticalacceleration vector using the telematics system.

In yet another additional embodiment of the invention, calculating thelateral acceleration vector further includes determining a lateralincline vector using a calibrated forward vector using the telematicssystem and calculating the lateral acceleration vector using thecalibrated forward vector and the lateral incline vector using thetelematics system.

In still another additional embodiment of the invention, the calibratedforward vector aligns the vehicular forward axis with the forward axisusing the telematics system.

In yet still another additional embodiment of the invention, calibratingacceleration information includes determining a vehicular lateral axisusing the telematics system, and aligning the vehicular lateral axiswith the lateral axis using the calibrated forward vector using thetelematics system.

In yet another embodiment of the invention, calculating the lateralacceleration vector further includes calculating a normalized crossproduct of the calibrated forward vector and the lateral incline vectorusing the telematics system.

In still another embodiment of the invention, calculating the forwardacceleration vector further includes determining a forward inclinevector using the telematics system and calculating the forwardacceleration vector using the forward incline vector and the lateralacceleration vector using the telematics system.

In yet still another embodiment of the invention, calculating theforward acceleration vector further includes calculating a normalizedcross product of the forward incline vector and the lateral accelerationvector using the telematics system.

In yet another additional embodiment of the invention, calculating thevertical acceleration vector is based on the lateral acceleration vectorand the forward acceleration vector using the telematics system.

In still another additional embodiment of the invention, calculating thevertical acceleration vector further includes calculating the normalizedcross product of the lateral acceleration vector and the forwardacceleration vector using the telematics system.

In yet still another additional embodiment of the invention, calibratingacceleration information includes determining an acceleration sensorvector including the forward acceleration information, the lateralacceleration information, and vertical acceleration information usingthe telematics system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system for calibrating a 3-axis accelerometer withan accelerometer, GPS unit and telematics processor in accordance withan embodiment of the invention.

FIG. 2 illustrates the alignment of the axes of a 3-axis accelerometerto the axes of a vehicle in accordance with an embodiment of theinvention.

FIG. 3 is a flow chart illustrating a process for calibrating the axesof an accelerometer to the vertical, forward and lateral axes of avehicle in accordance with an embodiment of the invention.

FIG. 4 is a flow chart illustrating a process for calibrating a 3-axisaccelerometer along its vertical vector in accordance with an embodimentof the invention.

FIG. 5 is a flow chart illustrating a process for calibrating a 3-axisaccelerometer along its lateral vector in accordance with an embodimentof the invention.

FIG. 6 is a flow chart illustrating a process for determining an averageforward vector used in the calibration of 3-axis accelerometer inaccordance with an embodiment of the invention.

FIG. 7 is a flow chart illustrating a process for the low latencycalibration of a 3-axis accelerometer in accordance with an embodimentof the invention.

FIG. 8 is a flow chart illustrating a process for the calibration of a3-axis accelerometer with vertical sample buffers in accordance with anembodiment of the invention.

DETAILED DESCRIPTION

Turning now to the drawings, systems and methods for low latencyacceleration alignment in order to reduce calibration delays intelematics systems in accordance with embodiments of the invention areillustrated. Information concerning vehicle speed and acceleration canprovide insights into driver behavior. For example, such information canindicate a variety of driver behaviors, including, but not limited to,performing hard cornering or suddenly stopping while driving. Inaccordance with many embodiments of the invention, vehicle speed may becalculated using information provided by a Global Position System (GPS)receiver by dividing the distance traveled by the GPS receiver by thetime between measurements taken by the GPS receiver. In a number ofembodiments, the GPS receiver is configured to determine headinginformation. In several embodiments, the GPS receiver is configured todetermine velocity information using the signals received by the GPSreceiver. A GPS receiver can determine velocity information in a varietyof ways in accordance with embodiments of the invention, including, butnot limited to, measuring the Doppler shift of the received signals. Thedifferences in vehicle speed between measurements taken by the GPSreceiver may be used to determine acceleration information for thevehicle. However, the use of GPS data to calculate accelerationinformation is dependent upon a variety of factors, such as receptionand satellite availability, which may present problems when calculatingthe acceleration information. In accordance with embodiments of theinvention, a variety of devices configured to determine location and/orvelocity information other than GPS receivers may be used.

Acceleration information for a vehicle may also be captured using anaccelerometer or other device configured to determine accelerationinformation; these devices are often installed on a vehicle or mobiledevice. Accelerometers installed on a vehicle may not be accuratelyaligned with the vehicle axes, limiting the accuracy of the accelerationdata captured by the accelerometer. In a number of embodiments, theaccelerometer axes do not change relative to the vehicle axes. A 3-axisaccelerometer is an accelerometer configured to determine accelerationin the X, Y, and Z axes, corresponding to the forward, lateral, andvertical vectors measured by the 3-axis accelerometer. Accurateaccelerometer data aligned with the axes of the vehicle is beneficial inmany applications, including, but not limited to, telematics. Telematicsis the integrated use of telecommunications and informatics, including,but not limited to, monitoring vehicle movement and behavior.

In accordance with embodiments of the invention, a 3-axis accelerometeris calibrated to align with a vehicle's vertical, lateral, and forwardaxes using acceleration information and location information of thevehicle. In many embodiments, the location information is captured usinga GPS receiver and the acceleration information is captured using the3-axis accelerometer, although other devices capable of capturinglocation and/or acceleration information may be utilized in accordancewith embodiments of the invention. These measurements may be taken basedupon an occurrence of certain events, in response to a request forcalibration, and/or performed continuously. In many embodiments,acceleration and location information is measured when locationinformation captured using the GPS receiver indicates that the vehicleis stationary. In several embodiments, acceleration and locationinformation is measured when the location information captures using theGPS receiver indicates that the vehicle is in motion and/or that thevehicle is traveling over a certain speed. Data analysis, includingfiltering, may be utilized to filter useful data from erroneous orirrelevant measurements captured by the 3-axis accelerometer and/or GPSreceiver and/or aligned data computed using the 3-axis accelerometerand/or GPS receiver data.

However, delays may be present in the calibration of vehicle axes toaccelerometer axes; such delays can be a function of the accumulatednumber of acceleration and/or velocity samples and the period over whichthe samples were accumulated. Telematics units in accordance withembodiments of the invention are configured to perform low latencycalibration of vehicle axes to accelerometer axes by determining lateralincline vectors and forward incline vectors using the velocity andacceleration information captured using the GPS receiver and the 3-axisaccelerometer. Using the lateral incline vector and the forward inclinevector, telematics units can quickly determine the aligned forward,lateral, and vertical vectors with a lower delay than computing thealigned forward, lateral, and vertical vectors using the accumulatedsamples. In a variety of embodiments, the calibration delay using thelateral incline vector and the forward incline vector is approximatelyhalf the sample period; however, other calibration delays are possiblein accordance with the requirements of embodiments of the invention.

Systems and methods for calibrating a 3-axis accelerometer to align withthe axes of a vehicle utilizing information captured using anaccelerometer and/or a GPS receiver in accordance with embodiments ofthe invention are discussed further below.

Telematics System Architecture

Telematics systems are utilized in vehicles to determine and/or reportthe location and behavior of the vehicle. A telematics system containinga 3-axis accelerometer aligned to vehicle axes in accordance with anembodiment of the invention is illustrated in FIG. 1. The telematicssystem 100 includes a telematics unit 102, where the telematics unit 102includes a GPS receiver 106, a 3-axis accelerometer 108, and atelematics process 110. The GPS receiver 106 and the 3-axisaccelerometer 108 are configured to communicate with a telematicsprocessor 110. The GPS receiver 106 is configured to receive signalsfrom one or more GPS satellites 104, if available. In accordance withembodiments of the invention, the GPS receiver 106 and the 3-axisaccelerometer 108 are configured to provide information to thetelematics processor 110 at a sample rate; the GPS sample rate of theGPS receiver 106 and the accelerometer sample rate of the 3-axisaccelerometer 108 are independent and determined dynamically orpre-determined.

In several embodiments, the GPS receiver 106 is configured to determinelocation information using signals received from a number of GPSsatellites 104. In many embodiments, the GPS receiver 106 is configuredto determine velocity and/or acceleration information using the receivedlocation information. In a number of embodiments, the GPS receiver isconfigured to determine velocity information by measuring the Dopplershift of the signals received from the GPS satellites 104. In a varietyof embodiments, a vertical sample buffer 114 is utilized to storevertical vector samples; the stored vertical vector samples can beprocessed to compensate for errors in the received GPS information. Inmany embodiments, the 3-axis accelerometer 108 can generate 3-axisacceleration data from vehicle motion. In many embodiments, thetelematics processor 110 is configured to calibrate the 3-axisaccelerometer 108 to correlate the 3-axis acceleration data generated bythe 3-axis accelerometer 108 to the axes of the vehicle in which thetelematics system 100 is installed using velocity and/or accelerationinformation. In a number of embodiments, the telematics processor 110 isconfigured to determine velocity and/or acceleration information usinglocation information received using the GPS receiver 106. In multipleembodiments, the telematics processor 110 utilizes acceleration and/orvelocity information generated by the GPS receiver 106.

In several embodiments, the telematics unit 102 includes a GPS samplefilter 120 and/or an accelerometer sample filter 124. The GPS samplefilter 120 is configured to sample and convert the sampling rate of theGPS receiver 106. The accelerometer sample filter 124 is configured tosample and convert the sampling rate of the 3-axis accelerometer 108. Inmany embodiments, the GPS sample filter 120 and/or the accelerometersample filter 124 are configured to match the GPS sampling rate to theaccelerometer sampling rate. For example, if the GPS receiver 106 has asampling rate of 250 milliseconds and the 3-axis accelerometer 108 has asampling rate of 50 milliseconds, the accelerometer sample filter 124can utilize five samples generated using the 3-axis accelerometer 108 tomatch the 250 millisecond sample rate of the GPS receiver 106. Theaccelerometer sample filter 124 and/or the GPS sample filter 120 performthe rate matching in a variety of ways, including, but not limited to,averaging information received, selecting the highest sample received,selecting the smallest sample received, selecting one sample at random,and/or selecting the last sample. In many embodiments, the accelerometersample filter 124 and/or the GPS sample filter 120 are implemented usingthe telematics processor 110 and/or the history buffer 112. In a varietyof embodiments, the sampling rates of the GPS receiver and theaccelerometer do not need to be synchronized in order to calibrate theaxes of the accelerometer with the vehicle axes.

In a number of embodiments, the telematics unit 102 includes a GPSsample window 122 configured to store one or more samples received usingthe GPS receiver 106. In several embodiments, the telematics unit 102includes an accelerometer sample window 126 configured to store one ormore samples received using the 3-axis accelerometer 108. In manyembodiments, the telematics processor 110 can accumulate informationprovided by the GPS receiver 106 and the 3-axis accelerometer 108 alongwith calibration information using a history buffer 112. In severalembodiments, the telematics processor 110 is configured to use theaccumulated information to calculate lateral incline vectors and forwardincline vectors. Using the lateral incline vectors and the forwardincline vectors, the telematics processor 110 is configured to performthe calibration of the 3-axis accelerometer 108 to the vehicle axes. Ina number of embodiments, the telematics processor 110 is configured toadapt the calibration of the 3-axis accelerometer 108 to the vehicleaxes using the location and/or velocity information determined using theGPS receiver 106. In many embodiments, the GPS sample window 122, theaccelerometer sample window 126, and/or the vertical sample buffer 114is implemented using the telematics processor 110 and/or the historybuffer 112.

A specific telematics system is described above; however, a variety oftelematics systems, including those that receive location informationwithout using a GPS receiver, may be utilized in accordance withembodiments of the invention. Processes for calibrating a 3-axisaccelerometer relative to the axes of a vehicle to which the 3-axisaccelerometer is installed are discussed further below.

Comparison of Accelerometer Axes and Vehicle Axes

In order to provide accurate acceleration information, a 3-axisaccelerometer is calibrated to the axes of the vehicle in which the3-axis accelerometer is installed. An illustration of the relativealignment of the axes of a 3-axis accelerometer to the axes of a vehiclein accordance with embodiments of the invention is shown in FIG. 2.Coordinate axes 200 show the relative alignment of the axes 208 of a3-axis accelerometer 204 and the axes 206 of a vehicle 202 to which theaccelerometer is mounted. The X, Y and Z coordinate axes 206 are theaxes of a vehicle. The X₁, Y₁ and Z₁ axes are the axes 208 of the 3-axisaccelerometer 204. In the illustrated embodiment, the axes 208 of the3-axis accelerometer 204 are not aligned with the axes 206 of thevehicle 202. Therefore, in order to determine acceleration along theaxes 206 of the vehicle, the 3-axis accelerometer's 204 axes 208 X₁, Y₁and Z₁ are calibrated with respect to the axes 206 X, Y and Z of thevehicle 202; processes for performing this calibration are discussed inmore detail below. In many embodiments of the invention, the axes 206 X,Y and Z of the vehicle 202 correspond to a gravity vector, a lateraldirectional vector of travel along a horizontal plane, and theorthogonal to the gravity vector and the lateral motion vector;accordingly, the calibration of the accelerometer's 204 axes 208 X₁, Y₁and Z₁ are to the gravity vector, the lateral motion vector, and theorthogonal of the gravity vector and the lateral motion vector. In manyembodiments, the 3-axis accelerometer 204 is part of a telematics systeminstalled in the vehicle 202.

Although a specific relative alignment between the axes of a 3-axisaccelerometer and a vehicle described above, a variety of alignments,including those where the axes of a 3-axis accelerometer are aligned toa gravity vector, a lateral motion vector, and the orthogonal of thegravity vector and the lateral motion vector, may be utilized inaccordance with embodiments of the invention. Processes for calibrating3-axis accelerometers in accordance with embodiments of the inventionare described below.

3-Axis Accelerometer Calibration Using GPS Location Information

The location, velocity, and acceleration of a vehicle can be capturedusing a GPS receiver and utilized to determine the motion of the axes ofa vehicle relative to the Earth. This information can be correlated toinformation measured using a 3-axis accelerometer, thereby calibratingthe 3-axis accelerometer to the vehicle. A process for calibrating theaxes of a 3-axis accelerometer to the vertical, forward and lateral axesof a vehicle containing both the 3-axis accelerometer and the GPSreceiver in accordance with an embodiment of the invention isillustrated in FIG. 3.

The process 300 includes determining (302) lateral acceleration. Forwardacceleration is determined (304). Vertical acceleration is determined(306). In several embodiments, orthogonal vectors representing thevertical, forward, and lateral vectors are computed (308). The vertical,forward, and lateral vectors are correlated (310) to the axes of the3-axis accelerometer. If necessary, the calibration process continues(312) beginning with step 302. If the calibration process does notcontinue (312), the process ends.

In many embodiments, lateral acceleration is determined (302) usinginformation captured using a 3-axis accelerometer when a GPS receiverindicates that the vehicle is not in motion. In a number of embodiments,forward acceleration is determined (304) using information measuredusing the 3-axis accelerometer when location information measured usingthe GPS receiver indicates that the vehicle is in motion. In severalembodiments, forward acceleration is determined (304) when a vehicleexceeds a predetermined speed. In several embodiments, verticalacceleration is determined (306) by computing the cross product of thelateral acceleration and forward acceleration. In many embodiments, theorthogonal vectors are computed (308) by calculating the cross productof every combination of the forward acceleration, the lateralacceleration, and the vertical acceleration. In a number of embodiments,calibration continues (312) if the magnitude of the correlation betweenthe 3-axis accelerometer and the vertical, forward, and lateral vectorsexceeds a threshold value. In several embodiments, the calibrationcontinues (312) while the vehicle is in motion. In many embodiments, thecalibration continues (312) while the vehicle is turned on. In a numberof embodiments, the calibration is only performed once and does notcontinue (312). In a number of embodiments, the calibration processcontinues (312) when the determined (302, 304, 306) lateral, forward,and/or vertical accelerations exceed a threshold value; the thresholdvalue may be pre-determined or determined dynamically. In severalembodiments, the calibration process continues (312) until a certainnumber of successful calibration attempts have been reached; the numberof successful calibration attempts may be pre-determined or determineddynamically.

In accordance with many embodiments of the invention, the determined(302, 304, 306) vertical, forward, and/or lateral accelerations arestored in a history buffer. Correlating (310) the vertical, forward, andlateral accelerations with the 3-axis accelerometer axes utilizes thestored vertical, forward, and/or lateral accelerations. In certainembodiments, once a new lateral acceleration is determined (302),correlating (310) the accelerations with the 3-axis accelerometer axesutilizes the lateral acceleration and forward and vertical accelerationsstored in the history buffer. Likewise, in several embodiments, once anew forward acceleration is determined (304), calibration (310) utilizesvertical and lateral accelerations stored in the history buffer. Invarious embodiments, the vertical, forward, and/or lateral accelerationsstored in the history buffer are used to predetermine what a vehicle'svertical, forward and lateral axes are and an accelerometer's axessystem are calibrated to fit the predetermined vehicle axes. In manyembodiments, the vertical, forward, and/or lateral accelerations storedin the history buffer correlate to GPS acceleration samples taken usingthe GPS receiver and/or accelerometer acceleration samples taken usingthe 3-axis accelerometer.

In accordance with embodiments of the invention, correlating (310) thevectors corresponding with the axes of the vehicle with the 3-axisaccelerometer axes may be performed using a least squares method. Givenmotion vector samples [X_(i), Y_(i), Z_(i)], where i is the number ofmotion vector samples, vertical alignment vector [V_(x), V_(y), V_(z)],forward GPS acceleration sample F and lateral GPS acceleration sampleL_(i) and vertical accelerationV _(i)=√{square root over (X _(i) ² +Y _(i) ² +Z _(i) ² −F _(i) ² −L_(i) ²)}the alignment vectors which calibrate the axes of the 3-axisaccelerometer to the axes of the vehicle are calculated by:B ₁ =A ₁₁ *V _(x) +A ₁₂ *V _(y) +A ₁₃ *V _(z)B ₂ =A ₁₂ *V _(x) +A ₂₂ *V _(y) +A ₂₃ *V _(z)B ₃ =A ₁₃ *V _(x) +A ₂₃ *V _(y) +A ₃₃ *V _(z)whereA ₁₁ =ΣX _(i) ²A ₁₂ =ΣX _(i) *Y _(i)A ₁₃ =ΣX _(i) *Z _(i)A ₂₂ =ΣY _(i) ²A ₂₃ =ΣY _(i) *Z _(i)A ₃₃ =ΣZ _(i) ²B ₁ =ΣV _(i) *X _(i)B ₂ =ΣV _(i) *Y _(i)B ₃ =ΣV _(i) *Z _(i)

In accordance with embodiments of the invention, the vertical alignmentvector[V_(x), V_(y), V_(z)] is determined using a Gaussian eliminationprocess. For example,

$V_{z} = \frac{{D_{2}*C_{11}} - {D_{1}*C_{12}}}{{C_{11}*C_{22}} - C_{12}^{2}}$$V_{y} = \frac{{D_{1}*C_{22}} - {D_{2}*C_{12}}}{{C_{11}*C_{22}} - C_{12}^{2}}$and V_(x) is the maximum of

$V_{x} = \frac{B_{1} - {A_{12}*V_{y}} - {A_{13}*V_{z}}}{A_{11}}$$V_{x} = \frac{B_{2} - {A_{22}*V_{y}} - {A_{23}*V_{z}}}{A_{12}}$$V_{x} = \frac{B_{3} - {A_{23}*V_{y}} - {A_{33}*V_{z}}}{A_{13}}$whereC ₁₁ =A _(1l) *A ₂₂ −A ₁₂ ²C ₁₂ =A ₁₁ *A ₂₃ −A ₁₂ *A ₁₃C ₂₂ =A _(1l) *A ₃₃ −A ₁₃ ²D ₁ =B ₂ *A ₁₁ −B ₁ *A ₁₂D ₂ =B ₃ *A ₁₁ −B ₁ *A ₁₃

Although a specific process for calibrating the axes of a 3-axisaccelerometer to the axes of a vehicle is discussed above with respectto FIG. 3, any of a variety of processes, including those which obtaininformation related to the location, velocity, and/or acceleration of avehicle using devices other than GPS receivers, may be performed inaccordance with embodiments of the invention. In particular, processesfor the low latency calibration of the axes of a 3-axis accelerometer tothe axes of the vehicle are discussed below with respect to FIG. 7.Processes for calibrating the axes of a 3-axis accelerometer inaccordance with embodiments of the invention are disclosed below.

Vertical Vector Calibration

Filtering the information measured using a 3-axis accelerometer, a GPSreceiver, and/or data aligning the 3-axis accelerometer and the GPSreceiver can eliminate erroneous data, including, but not limited to,data from a vehicle stopped on an incline. A process for calibrating avertical vector measured using a 3-axis accelerometer to filtererroneous data in accordance with an embodiment of the invention isillustrated in FIG. 4. The process 400 includes measuring (402) verticalacceleration using a 3-axis accelerometer. The forward acceleration ofthe 3-axis accelerometer is measured (404). The forward acceleration andthe vertical acceleration are processed (406) to determine a verticalvector. In several embodiments, the vertical acceleration and/or theforward acceleration are stored (408) as part or all of the historicalmotion data. If the vertical vector is detected (410) in the processed(408) vertical and forward accelerations, the 3-axis accelerometercalibration is updated (412) to compensate for the vertical vector. In anumber of embodiments, if a vertical vector is not detected (410), theprocess 400 repeats. In many embodiments, if a vertical vector is notdetected (410), the process 400 ends.

In many embodiments, the vertical vector is measured (402) when thespeed of the vehicle exceeds a threshold; the threshold may bepre-determined or determined dynamically. In several embodiments, theforward acceleration of the 3-axis accelerometer is measured (404) whenthe forward acceleration exceeds a threshold acceleration; the thresholdacceleration may be pre-determined or determined dynamically. In anumber of embodiments, the motion of the vehicle is determined using aGPS receiver. In several embodiments, elevation data measured using theGPS receiver is utilized to determine whether the vehicle is likelystopped on an incline. In many embodiments, determining that the vehicleis at rest using the GPS receiver involves no change in GPS receiverposition over time. In a number of embodiments, detecting no GPSreceiver movement can involve a determination of whether there is anyGPS receiver movement over time that takes consideration of erroneousGPS receiver movement readings. In many embodiments, the motion of thevehicle is determined using the 3-axis accelerometer. In severalembodiments, detecting constant acceleration using an accelerometer ismade in an event with no movement of a vehicle as detected by a GPSreceiver. In several embodiments, the stored (408) historical motiondata includes data captured using the GPS receiver and/or 3-axisaccelerometer. In certain embodiments, only a selection of data isstored (408) as historical motion data, such as data that corresponds tocertain events of interest. In a number of embodiments, all datacaptured using the GPS receiver and/or 3-axis accelerometer is stored(408) as historical motion data.

For example, when the GPS receiver indicates that a vehicle isstationary and the 3-axis accelerometer experiences constantacceleration, an assumption can be made that the vehicle is stationaryand that the 3-axis accelerometer output is indicative of verticalacceleration due to gravity. When both the 3-axis accelerometer and theGPS receiver indicate vehicle speeds above a certain threshold value andincreasing with a constant direction, an assumption can be made that thevehicle is accelerating in approximately a straight line. When acalibration event occurs, the calibration of the 3-axis accelerometer isupdated (412) utilizing the determined (406) vertical vector tocompensate for the vertical acceleration due to gravity as measured bythe 3-axis accelerometer.

In numerous embodiments, the processing (406) of current motion dataincludes analysis and filtering of data to provide data veracity. Inseveral embodiments, current measured (402, 404) vertical and forwardaccelerations are processed (406) using historical motion data. Dataanalysis can utilize filters, including least mean squares, leastsquares, and Gaussian elimination methods, including those describedabove with respect to FIG. 3.

Although specific processes are discussed above for calibrating a 3-axisaccelerometer to compensate for acceleration along its vertical vector,any of a variety of processes can be utilized, including processes thatoperate on vehicles that are in motion, in accordance with embodimentsof the invention. In particular, alternative techniques for calibratinga 3-axis accelerometer that utilize vertical sample buffers tocompensate for measurement errors in the vertical vector are discussedin more detail below with respect to FIG. 8 and processes for the lowlatency determination of vertical alignment information are discussedbelow with respect to FIG. 7. Processes for calibrating a 3-axisaccelerometer along its forward vector in accordance with embodiments ofthe invention are described below.

Lateral Vector Calibration

Filtering the lateral vector measured by a 3-axis accelerometer allows atelematics unit to compensate for measurement errors, includingmeasurements made when a vehicle is moving backwards or turning veryslightly. A process for calibrating a 3-axis accelerometer along itslateral axis in accordance with an embodiment of the invention isillustrated in FIG. 5. The process 500 includes detecting (502) datarelated to the forward acceleration of a vehicle. The direction of theacceleration is determined (504). The acceleration data is processed(506) to determine a lateral vector. In a number of embodiments, theacceleration data is stored (508) as part of all of the historicalmotion data. If a lateral vector is detected (510), the calibration ofthe 3-axis accelerometer is updated (512) using the lateral vector. Inmany embodiments, if no lateral vector is detected (510), the process500 repeats. In several embodiments, if no lateral vector is detected(510), the process 500 is complete.

In many embodiments, detecting (502) data related to the forwardacceleration of a vehicle includes determining that the velocity of thevehicle exceeds a threshold velocity. In several embodiments, thevelocity of the vehicle may be detected (502) using a GPS receiverand/or a 3-axis accelerometer. The GPS receiver and/or 3-axisaccelerometer may also be utilized to determine (504) the direction inwhich the vehicle is traveling. In a number of embodiments, the vehicleis traveling in a constant direction. Analysis of data received using aGPS receiver can determine (504) whether the direction of motion isunchanging by comparing current values to past values. Similarly,analysis of data received using a 3-axis accelerometer can determine(504) whether the direction of acceleration is unchanging by comparingcurrent acceleration to past values for any changes in accelerationdirection. Certain embodiments only use a GPS receiver or only use a3-axis accelerometer to determine (504) constant direction; otherembodiments use both a GPS receiver and a 3-axis accelerometer todetermine (504) a constant direction. Several embodiments use a GPSreceiver to check data received using a 3-axis accelerometer or viceversa. In various embodiments, a constant direction is not one in whichdata indicates the direction data is rigidly constant, but takes intoaccount errors and discrepancies that may come from erroneous directiondata, such as an inaccurate GPS reading or measurement errors in a3-axis accelerometer.

Analysis of data can be used to determine whether the data is indicativeof a lateral vector. Indications of a lateral vector can filter out datathat is likely an outlier, such as data indicating that a vehicle ismoving backward rather than forward. This can include filtering outevents indicating that a vehicle is slowly backing out of a parking spotbefore turning and driving in a forward direction. Data analysis canutilize filters, including, but not limited to, least mean squares,least squares, and Gaussian elimination methods, including thosedescribed above with respect to FIG. 3.

A specific process is described above with respect to FIG. 5 forcalibrating the forward axis of a 3-axis accelerometer with respect to alateral vector; however, any of a variety of processes can be utilized,including processes that do not rely upon uniform forward motion of thevehicle, in accordance with an embodiment of the invention. Processesfor the low latency calibration of the forward axis of a 3-axisaccelerometer using lateral incline vectors in accordance withembodiments of the invention are discussed below with respect to FIG. 7.Processes for calibrating a 3-axis accelerometer using an averageforward vector in accordance with embodiments of the invention arediscussed below.

3-Axis Accelerometer Calibration Using an Average Forward Vector

Once a vertical vector and/or a lateral vector have been determined, anaverage forward vector can be computed; this average forward vector isused to calibrate the forward acceleration measured using a 3-axisaccelerometer to the forward motion of the vehicle in which the 3-axisaccelerometer is mounted. A process for determining an average forwardvector used to calibrate a 3-axis accelerometer in accordance with enembodiment of the invention is illustrated in FIG. 6. The process 600includes determining (602) acceleration information. A vertical vectoris determined (604). An average forward vector is determined (606). Inmany embodiments, the vertical, lateral, and/or average forward vectorsare stored (608) as historical data. The calibration of a 3-axisaccelerometer is updated (610).

In many embodiments, acceleration information is determined (602)utilizing a GPS receiver and/or a 3-axis accelerometer. In manyembodiments, the vertical vector is determined (604) using a processsimilar to the one described above with respect to FIG. 4. In a numberof embodiments, determining (604) the vertical vector includesmultiplying a normalized vertical vector by acceleration informationstored as historical data. In several embodiments, determining (606) theaverage forward vector includes determining a lateral vector using aprocess similar to the one described above with respect to FIG. 5. Inmany embodiments, determining the lateral vector includes subtractingthe determined (604) vertical vector from the determined (602)acceleration information. The vertical vector and/or accelerationinformation used to determine the lateral vector may be stored (608) ashistorical data. In a number of embodiments, determining (606) theaverage forward vector utilizes the lateral vector and the angle betweenthe lateral vector and a measured forward vector. In severalembodiments, the measured forward vector is determined using forwardacceleration information captured using a 3-axis accelerometer. In manyembodiments, the measured forward vector is a previously calculatedaverage forward vectored stored as historical data. In a number ofembodiments, determining (606) the average forward vector uses one orboth of the determined (602) acceleration and the determined (604)vertical vector. In many embodiments, a certain amount of accelerationinformation and/or a certain number of vertical vectors and/or averageforward vectors are stored (608) as historical data before the 3-axisaccelerometer calibration is updated (610). The amount of accelerationinformation and/or number of vectors stored may be determineddynamically and/or pre-determined.

A specific process is described above with respect to FIG. 6 forcalibrating a 3-axis accelerometer using a determined average forwardvector; however, any of a variety of processes, including those whichutilize an average lateral vector and those which determine a lateralvector, can be utilized in accordance with an embodiment of theinvention. Processes for a low latency determination of alignmentinformation are discussed below.

Low Latency 3-Axis Accelerometer Calibration

During the operation of a vehicle, drivers benefit from receivingwarning and alerts as quickly as possible so corrective action can betaken. Many of these alerts depend upon acceleration informationmeasured using 3-axis accelerometers. By performing a low latencyalignment of a 3-axis accelerometer, acceleration information can beprovided quickly, enabling warnings and alerts to be generated withshort delays. Telematics units in accordance with embodiments areconfigured to determine lateral incline vectors and forward inclinevectors using measured acceleration information; these vectors can beutilized to determine alignment information in a low latency fashion. Aprocess for low latency acceleration alignment in accordance with anembodiment of the invention is shown in FIG. 7. The process 700 includesmeasuring (702) forward and lateral acceleration. A lateral inclinevector is calculated (704). A lateral vector is calculated (706). Aforward incline vector is calculated (708). A forward vector iscalculated (710). A vertical vector is calculated (712). Accelerationaxes are calibrated (714).

In a variety of embodiments, measuring (702) forward and/or lateralacceleration is performed using a GPS receiver and/or 3-axisaccelerometer. In several embodiments, measuring (702) forward and/orlateral acceleration is performed using processes similar to thosedescribed above. In many embodiments, a lateral incline vector(A_(lat-incline)) can be calculated (704) such that:A _(lat-incline) =A _(mems) −L _(gps)*Norm(F _(calb) ×A _(mems))where A_(mems) is a vector representing the acceleration data typicallyprovided by a 3-axis accelerometer, F_(calb) is the calibrated forwardvector, and L_(gps) is the lateral acceleration of a vehicle. In anumber of embodiments, L_(gps) is determined using a GPS receiver. Inseveral embodiments, A_(lat-incline) is calculated by determining theaccelerometer acceleration vector (A_(mems)) and forward vector(F_(calb)) and computing the cross product of the two vectors. In avariety of embodiments, the resulting vector is normalized.

In several embodiments, a lateral vector (A_(lat)) can be calculated(706) using the formula:A _(lat)=Norm(F _(calb) ×A _(lat-incline))where F_(calb) is the calibrated forward vector and A_(lat-incline) isthe lateral incline vector.

In a similar fashion, in several embodiments of the invention, a forwardincline vector (A_(forw-incline)) can be calculated (708) such that:A _(forw-incline) =A _(mems) −F _(gps)*Norm(A _(lat-incline) ×A _(lat))where A_(lat-incline) is the lateral incline vector, A_(lat) is thelateral vector, F_(gps) is the measured forward acceleration, andA_(mems) is the acceleration vector. In a variety of embodiments,(A_(lat-incline)×A_(lat)) is normalized.

In many embodiments, the forward vector (A_(forw)) can be calculated(710) such that:A _(forw)=Norm(A _(forw-incline) ×A _(lat))where A_(forw-incline) is the forward incline vector and (A_(lat)) thelateral vector. In a variety of embodiments (A_(forw-incline)×A_(lat))is normalized to determine the forward vector (A_(forw)). Once thelateral and forward vectors are calculated, the vertical vector(A_(vert)) may be calculated (712) such that:A _(vert)=Norm(A _(lat) ×A _(forw))where A_(lat) is the lateral vector and A_(forw) is the forward vector.In a variety of embodiments (A_(lat)×A_(forw)) is normalized todetermine the vertical vector (A_(vert)).

In a variety of embodiments, the axes of the 3-axis accelerometer arecalibrated (714) to the axes of the vehicle using the aligned (706, 710,712) forward, lateral, and vertical vectors. In several embodiments ofthe invention, the aligned lateral vector (A_(lat)), forward vector(A_(forw)), and vertical vector (A_(vert)), are used to calibrate (714)the aligned lateral, forward, and vertical axes such that:Aligned Lateral Axis=A _(lat) *A _(mems)Aligned Forward Axis=A _(forw) *A _(mems)Aligned Vertical Axis=A _(vert) *A _(mems)

As discussed above, the acceleration information utilized above isobtained from 3-axis accelerometers and GPS receivers at a sampling raterelated to the device providing the information. In many embodiments,the determination of the lateral incline vector and the forward inclinevector utilizes fewer samples (a variety of embodiments utilize half thenumber of samples) than accumulating information from the 3-axisaccelerometer and the GPS receiver and directly calculating thecalibration information for the forward, lateral, and vertical axes ofthe 3-axis accelerometer and the vehicle using the accumulated sampleswhile maintaining equivalent performance in the calibration. Byutilizing fewer samples to determine the alignment information used tocalibrate the 3-axis accelerometer to the vehicle axes, telematicssystems utilizing lateral incline vectors and forward incline vectors inthe calibration as described above exhibit low latency in thecalibration of the 3-axis accelerometer to the vehicle axes.

Although specific processes for the low latency calibration of thealigned lateral, forward, and vertical vectors are discussed above withrespect to FIG. 7, any of a variety of processes, including thoseutilizing alternative methods for determining accelerations other thanGPS receivers and 3-axis accelerometers, can be utilized in accordancewith embodiments of the invention. Processes for alignment methodsutilizing vertical sample buffers in accordance with embodiments of theinvention are discussed further below.

Acceleration Alignment with Vertical Sample Buffers

Information determined via a GPS receiver can include measurement errorsunique to each sample of information obtained; these errors induceadditional noise and errors in the calibration of 3-axis accelerometersusing the GPS-determined acceleration data. Telematics units inaccordance with embodiments of the invention are configured to utilizevertical sample buffers to determine an average vertical vector thatcompensates for the measurement errors in the samples obtained from theGPS receiver. A process for utilizing vertical vector stabilization inthe calibration of 3-axis accelerometers in accordance with anembodiment of the invention is shown in FIG. 8. The process 800 includesdetermining (802) vertical acceleration vectors. One or more verticalacceleration vectors are stored (804). If the number of stored vectorsdoes not exceed (806) a threshold value, more vertical accelerationvectors are determined (802). If the number of stored vectors exceeds(806) a threshold value, an average acceleration vector is calculated(808). The threshold value can be determined dynamically and/or bepredetermined. The average acceleration vector is processed. An averagevertical vector (810) is determined. Corresponding motion samples arealigned (812).

In a variety of embodiments, determining (802) vertical accelerationvectors is performed using processes similar to those described above.In a number of embodiments, the determined (802) vertical accelerationvectors are measured using a GPS receiver. In several embodiments, thedetermined (802) vertical acceleration vectors are stored (804) using avertical sample buffer. In many embodiments, the vertical sample bufferis a circular buffer; circular buffers in accordance with embodiments ofthe invention are configured to store a number of vertical accelerationvectors. Once the circular buffer has reached its capacity, the oldestvector is dropped (or overwritten) and a new vertical accelerationvector takes its place. In several embodiments, the vertical samplebuffer is configured to associate metadata including, but not limited toa timestamp, with a particular vertical acceleration vector. Once thevertical sample buffer has reached its capacity, the metadata isutilized to determine which vertical acceleration vector is dropped (oroverwritten). The capacity of the vertical acceleration buffer can bepredetermined and/or determined dynamically. Other buffers and bufferingtechniques can be utilized according to the requirements of embodimentsof the invention.

In many embodiments, the average acceleration vector is calculated (808)by accumulating the previous calculated vertical vectors and updatingthe average using each newly calculated vector utilizing a counter. Inseveral embodiments, the stored vertical acceleration vectors aredetermined during different periods of time and include varyingmeasurement errors. In a variety of embodiments, determining (810) anaverage vertical vector includes calculating a moving average using thestored (804) vertical acceleration vectors. In a number of embodiments,an average of the stored (804) vertical acceleration vectors is used todetermine (810) the average vertical vector. The number stored (804)vertical acceleration vectors utilized to determine (810) the averagevertical vector can be all of the stored (804) vectors or a portion ofthe stored (804) vectors. In a number of embodiments, the determined(810) average vertical vector is used to align (812) the correspondingmotion samples by determining forward and lateral vectors using methodsincluding, but not limited to, those discussed above. Utilizing thedetermined (810) average vertical vector, errors in the measurement ofthe vertical vectors are limited and aid in the accurate alignment (812)of the corresponding motion samples.

Although specific processes for performing acceleration alignment usingvertical sample buffers are discussed above with respect to FIG. 8, anyof a variety of processes appropriate to the requirements of a specificapplication can be utilized in accordance with embodiments of theinvention.

Although the present invention has been described in certain specificaspects, many additional modifications and variations would be apparentto those skilled in the art. It is therefore to be understood that thepresent invention may be practiced otherwise than specifically describedwithout departing from the scope and spirit of the present invention.Thus, embodiments of the present invention should be considered in allrespects as illustrative and not restrictive. Accordingly, the scope ofthe invention should be determined not by the embodiments illustrated,but by the appended claims and their equivalents.

What is claimed is:
 1. A telematics system, comprising: a processor; anacceleration sensor connected to the processor, wherein the accelerationsensor is a 3-axis accelerometer configured to determine an accelerationsensor vector comprising forward acceleration information along aforward axis, lateral acceleration information along a lateral axis, andvertical acceleration information along a vertical axis, wherein theforward axis, the lateral axis, and the vertical axis are defined by afirst orientation of the acceleration sensor; a velocity sensor mountedto a vehicle and connected to the processor and configured to determinevelocity information along a vehicular forward axis and headinginformation, wherein the vehicular forward axis is defined by a secondorientation of the vehicle and the heading information is relative tothe second orientation of the vehicle; and a memory connected to theprocessor and configured to store an acceleration alignment application;wherein the acceleration alignment application configures the processorto: determine vehicular forward acceleration information along thevehicular forward axis using the velocity information; determinevehicular lateral acceleration information using the velocityinformation and the heading information; determine a lateral inclinevector as a difference of the acceleration sensor vector and a dotproduct of the vehicular lateral acceleration information with anormalized cross product of a calibrated forward vector and theacceleration sensor vector; calculate a lateral acceleration vector as anormalized cross product of the calibrated forward vector and thelateral incline vector; determine a forward incline vector as adifference of the acceleration sensor vector and a dot product of thevehicular forward acceleration information and a normalized crossproduct of the lateral incline vector and the lateral accelerationvector; calculate a forward acceleration vector as a normalized crossproduct of the forward incline vector and the lateral accelerationvector; calculate a vertical acceleration vector as a normalized crossproduct of the lateral acceleration vector and the forward accelerationvector; compute lateral alignment information as a dot product of thelateral acceleration vector and the acceleration sensor vector; computeforward alignment information as a dot product of the forwardacceleration vector and the acceleration sensor vector; and computevertical alignment information as a dot product of the verticalacceleration vector and the acceleration sensor vector; wherein thelateral alignment information, the forward alignment information, andthe vertical alignment information calibrate the first orientation ofthe acceleration sensor to the second orientation of the vehicle.
 2. Thetelematics system of claim 1, wherein the calibrated forward vectoraligns the vehicular forward axis with the forward axis.
 3. Thetelematics system of claim 2, wherein: the acceleration alignmentapplication further configures the processor to determine a vehicularlateral axis using the heading information and the vehicular forwardacceleration information; and the calibrated forward vector furtheraligns the vehicular lateral axis with the lateral axis.
 4. A method forcalibrating axes of an acceleration sensor using a telematics system,where the telematics system is mounted in a vehicle having a vehicularforward axis, a vehicular lateral axis, and a vehicular vertical axis,the method comprising: determining, by the telematics system, vehicularforward acceleration information along the vehicular forward axis usinga velocity sensor of the telematics system; determining, by thetelematics system, vehicular lateral acceleration information along thevehicular lateral axis using the velocity sensor of the telematicssystem; determining, by the telematics system, a lateral incline vectoras a difference of an acceleration sensor vector and a dot product ofthe vehicular lateral acceleration information with a normalized crossproduct of a calibrated forward vector and the acceleration sensorvector, wherein the acceleration sensor vector is determined by anacceleration sensor of the telematics system, and wherein theacceleration sensor vector comprises forward acceleration informationalong a forward axis, lateral acceleration information along a lateralaxis, and vertical acceleration information along a vertical axis;calculating, by the telematics system, a lateral acceleration vector asa normalized cross product of the calibrated forward vector and thelateral incline vector; determining, by the telematics system, a forwardincline vector as a difference of the acceleration sensor vector and adot product of the vehicular forward acceleration information and anormalized cross product of the lateral incline vector and the lateralacceleration vector; calculating, by the telematics system, a forwardacceleration vector as a normalized cross product of the forward inclinevector and the lateral acceleration vector; calculating, by thetelematics system, a vertical acceleration vector as a normalized crossproduct of the lateral acceleration vector and the forward accelerationvector; computing, by the telematics system, lateral alignmentinformation as a dot product of the lateral acceleration vector and theacceleration sensor vector; computing, by the telematics system, forwardalignment information as a dot product of the forward accelerationvector and the acceleration sensor vector; and computing, by thetelematics system, vertical alignment information as a dot product ofthe vertical acceleration vector and the acceleration sensor vector,wherein the lateral alignment information, the forward alignmentinformation, and the vertical alignment information calibrate axes ofthe acceleration sensor to axes of the vehicle.
 5. The method of claim4, wherein the calibrated forward vector aligns the vehicular forwardaxis with the forward axis using the telematics system.
 6. The method ofclaim 5, further comprising: aligning the vehicular lateral axis withthe lateral axis using the calibrated forward vector using thetelematics system.